"The shifts of some quasars suggest they are receding at about 90% of the speed of light, and if this is true they are about 12 billion light-years away."

12 billion light-years

Sagan, Carl. Cosmos. New York: Ballantine, 1980: 216.

"The nearest is perhaps half a billion light-years away. The farthest mat be ten to twelve or more billions."

12 billion light-years

Quasar is short for quasi-stellar radio source. They are very
faint, intensely blue galaxy-like formations that emit large amounts
of energy and strong radio signals. In the late 1950s quasars
were first discovered with radio telescopes. Later on optical
images that matched the positions of the radio sources were found.
The brightest quasar is 3C 273 which lies at a distance of 2 billion
light-years away.

The properties of quasars are still very obscure. The sudden
shift of the emission lines from blue to red (the longest wavelengths),
discovered in 1963, puzzled astronomers. This radical red shift
has been interpreted as a Doppler effect, that is, and increase
in wavelength due to motion. This increase indicates the quasars
are traveling away from us at incredible speeds. But a few astronomers
have argued that the red shifts are not cosmological in origin
and do not indicate the distances of quasars.

On the other hand, these red shifts suggest that some quasars
are receding at a speed of 90 percent the speed of light. According
to Hubble's law of expansion of the universe, these large velocities
correspond to large distances. No quasars are found with 2 billion
light-years. Therefore, quasars are the most distant known objects
in the universe ranging from 2 billion to 12 billion light-years
away.

"With the estimated distance of 12.5 billion light years for STIS 123627+621755 no longer correct, the new title holder for the most distant object known belongs to a quasar, an active black hole at 12.4 billion light years."

"A team of astronomers may have discovered the most distant galaxy in the universe. Located an estimated 13 billion light-years away, the object is being viewed at a time only 750 million years after the big bang, when the universe was barely 5 percent of its current age …. Analysis of a sequence of Hubble images indicate the object lies in between a redshift of 6.6 and 7.1, making it the most distant source currently known. However, long exposures in the optical and infrared taken with spectrographs on the 10-meter Keck telescopes suggests that the object has a redshift towards the upper end of this range, around redshift 7."

"Named Abell 1835 IR1916, the newly discovered galaxy has a redshift of 10 [3] and is located about 13,230 million light-years away. It is therefore seen at a time when the Universe was merely 470 million years young, that is, barely 3 percent of its current age."